Method of and apparatus for heat-treating



Jan. 25, 1949. F. o. HEss Y 2,460,085

METHOD OF AND APPARATUS FOR HEAT TREATING Filed Deo. 14, 1944 ,c5/1p?. i

/NVENTOR Q0 M@ /fa WITNESS y5y Patented Jan. 25, 1949 METHOD F AND APPARATUS FOR HEAT-TREATING vFrederic O. Hess, Philadelphia, Pa., assignor to Selas Corporation of America, Philadelphia, Pa., a corporation of Pennsylvania Application December 14, 1944, Serial No. 568,145

(Cl. 263-2) f 4 Claims.

-1 My invention relates to a method of and apparatus for heat treating metallic bodies, and particularly to an open arrangement for selectively heat treating metallic bodies with a combustible gas mixture. A

When using gaseous fuel for heat treating and hardening operations. it has generally been the .practice heretofore to employ a mixture of oxygen and acetylene, and to provide one or more burner tips for using such mixture to produce a single high temperature Oxy-acetylene flame or a number of such flames which are grouped together and moved repeatedly over the work surfaces to be heat treated or hardened to bring such areas to an elevated temperature for a desired depth. When automatically accomplishing heat treating and hardening operations in this manner, it is necessary to provide suitable mechanism to obtain the desired relative movement between the burner tips and work surfaces while heat treating is being effected. This becomes troublesome and does not lend itself to continuous processing of work pieces, and this is particularly the case when such mechanism must be provided for progressively heat treating successive surface portions of irregular-shaped metallic bodies.

Further, heating metallic bodies with oxyacetylene burners has serious limitations in many heating operations because of the one requirement of maintaining the workin immediate proximity to the tips of the burner flames. This requirement for precisely locating the work surfaces to be heated with respect to the tips ofoxyacetylene flames presents an exceedingly difficult problem in many cases, and this is especially true where it is desired to heat treat or harden work in a continuous process.

In accordance with this invention, the parts of work pieces to be heat treated or hardened are positioned in a recess or work receiving space having a refractory lining so as to form a relatively narrow gap therebetween, and a stream of `r`high temperature gases, which consists substankwith the work surfaces.

In order to develop and produce large volumes of such heated gases, the slot or work receiving space is formed with a restricted opening communicating with a substantially closed chamber having an inner wall surface formed of refractory material. Combustion of a suitable combustible gas mixture is accomplished in the chamber which heats the inner wall surface thereof to incandescence, and, as a result of the intense radiant heat emitted from the highly heated incandescent wall surface, the gas mixture is completely burned-in the chamber and the products of combustion developed are heated to the highest ipossible temperature.

These heated gases then pass from the chamber through the restricted opening into the narrow gap between the lining of the work receiving space and the work piece positioned therein. Since the chemical reaction of combustion is substantially completed in the chamber, large volumes of highly heated gases are immediately available for heating work; and the precise location of the work in the work receiving space' is not critical, because heat is transferred to the work from the refractory lining which is heated to a highly radiant condition by the heated gases coming in contact therewith and by heat liberated from such heated gases sweeping over the work surfaces.

The invention is especially useful for carrying `out heal'l treating or hardening operations with a combustible gaseous mixture of air and a gas, such as, for example, ordinary city gas, natural gas and the like. Even though the theoretical flame temperature of a gas mixture of air and city gas, having a rating of about 500 B. t. u. per cubic foot, is approximately 3700* F., it is possible in practicing the invention to develop and produce temperatures of 2850 F. and higher at a refractory wall surface which is co-extensive in area with that ofthe work surface to be heat treated or hardened, whereby all portions of the work surface to be heat treated can be heated to the desired elevated temperature by a steady and continuous application of heat without the necessity of repeatedly moving a heating source back and forth over successive portions of the work surfaces.

Although I do not wish to be limited thereto, it is my belief that rapid heat treatment of ferrous metallic bodies to the critical hardening temperature of about 1650 F. in a matter of a few minutes, in accordance with the principles of the invention, is due to the exceptionally rapid heat penetration into the work surfaces being heat treated. This rapid heat penetration is obtained spectrum and of a wave-length not greater than two microns. This radiant energy, together ywith the high velocity stream of heated products of combustion passing through the' gap formed between the refractory surfaces and the work, pro-f duces and develops temperatures of 2850 F. and

@higher but materially below the temperatures developed by Oxy-acetylene flames, whereby safe heat penetration is accomplished without the likelihood of injuring the work even when all of the work surfaces to be heat treated or hardened are heated simultaneously and brought to the desired elevated temperature by steady and continuous application of heat. t y

The invention, together with the objects and advantages thereof, will be more fully understood from the following description and accompanying drawings forming a part of this specication', and of which:

Fig. 1 is a vertical sectional View of a heating unit embodying the invention;

Fig. 2 is another sectional view, taken at rightangles to Fig. 1; and

Figs. 3, 4 and 5 are fragmentary sectional views of heating units similar to that shown'in Fig. l, illustrating other embodiments of the invention.

Referring to Figs. 1 and 2 of the drawing, a

heating unit IIJ for practicing the invention comprises a recess or slot I I having a refractory lining I2 which serves as a work receiving space to receive the portion I4 of a work piece I5 adapted such as water, for example. `may be circulated through inlet-and outletfopenings 22, only one of which is shown, to eect cooling and prevent excessive heating of the metallic shell.

The heating unit y I8 includes a hollow base member 23 having several cross partitions 2l to vform a plurality of inlet chambers 28. The xnember 23 is formedto receive a burner screen or orifice member 26 having a plurality of openings or passages 21. The burner screen 28 may com prise a pluralityof relatively thin plates stacked and closely held together. One face of each plate may be formed with a plurality of slots. of

relatively narrow depth and the plates stacked together with the slotted face of each plate, except one end plate, contiguous to and contacting a smooth face of an adjacent plate. A combustible fuel mixture from a suitable source of supply is introduced through inlet openings 28 into Athe inlet chambers 25, so that the fuel mixture may I `fractory wall surface I9 that the latter is heated to a highly radiant condition. Due to heating the 'inner wall surfaces I9 to a high incandescent temperature, and subjecting the fuel mixture entering the combustion chamber to intense heat to be heat treated to the critical hardening tem- I perature of about 1650 F. In Figs. I and 2 the work piece I5 represents a part of a tank grouser which is formed of ferrous metal and subjected to considerable wear. i

The work piece I5 is positioned in the slot II so that a narrow gap I6 is formed between the lining I2 and portion I4 of the work piece to be and in which substantially complete combustion of a gaseous mixture is accomplished. In this way a high temperature gas stream, in which the chemical reaction of combustion is completed, is made available to heat the refractory lining I2 to a highly radiant condition for heat treating or hardening the surfaces of work pieces at close range in an open arrangement which lends itself for heat treating work pieces in av continuous process.

In accordance wi'th this invention, therefore, the opening I1 is co-extensive with the length of the work piece I 5, as best seen in Fig.y 2, and constitutes a restricted outlet of the substantially closed combustion chamber I8 having aninner wall surface I 9 of refractory material. The combustion chamber I8 is formed by a hollow refractory body 20 about which is provided an outer protective casing or shell 2| which may be hollow and through which a suitable cooling medium,-

radiated-from the highly incandescent wall sur- -face I9, substantially complete combustion of the fuel is accomplished in the chamber I8 before the mixture reaches the restricted outlet or opening I1. From the restricted opening I1 is discharged a'high velocity jet or stream of heated gases consisting substantially entirely of heated products of combustion.

'Ihe hollow body 20 is formed of ceramic material Y and possesses such thermal properties that a poor heat conductive path is providedv through the refractory wall. so that the heat loss therethrough will be at a minimum. Not only does the refractory body 20 form an inner refractory wall surface for the chamber I8 but also -gases are discharged from chamber I8 in a gas y stream having anaverage velocity of 700 feet per inches to sixty inches of water column in excess of the pressure at the discharge end of the outlet.

Due to such heating the gases 'By maintaining the chamber at suchv an excess pressure. the rate of combustion in chamber Il is accelerated and the temperature at which combustion takes place is increased, lso that heated gases are made availablefor heating work pieces to the hardening temperature' in the shortest length of timeposslble. During normal operation the refractory material defining the opening I1 becomes heated to incandescence by the heated gases coming in contact therewith, so that the heated gases are discharged from chamber I8 at a temperature nearly equal tothe temperature produced and maintained in combustion chamber Il.

I have found that this high temperature stream A vof heated gases can be eectively utilized to accomplish selective heat treating or hardening operations in an open arrangement by causing such heated gases to heat to ahighly radiant condition the lining I2 ofthe recess II in which is positioned the work piece` I5 to be heat treated. When a mixture of air and ordinary city gas is employed, for example, the liningA I2 may be' heated to a white incandescent temperature of 2850o F. and higher which is practically equal to the temeerature 'at which the combustion chamber I8 is maintained.v Further, these high temperature gases, which spread out in the gap I6. flow at a relatively high velocity over the surface portions Il to be heattreated and contribute to the high rate of heat transfer to the work. In heating the work piece I5 like the tank grouser illustrated, for example, in which the gap may be between onefourth to three-fourths inch in size, I havefound that the portions Il can be heated to the critical hardening temperature of 1650 F. in about eighty Aseconds when using a gas mixture of air and ordinary city gas. 1

This rapid heat treatment of ferrous metallic. bodies is, I believe, vdue to the rapid heat penetration into the work surfaces being heat treated as the result of the transmission of a major portion of the heat from a refractory wall surface which is located at close range tothe work andin a tional to the difference of the absolute temperatures raised to the fourth power, it will be evident that the use of high temperature gases for heating lining I2 immediately upon being discharged from the opening I1 is an important factor contributing to the rapid heat treatment of work pieces.

Further, these heated gases in spreading and passing through the gap I6 blanket and protect the lining I2 from the surrounding cooler atmosphere whereby the lining will always-be malntained at a high incandescent temperature. QThus, the positioning of the work in the recess or slot I I to place the portion I4 at close range to the lining I2 is another important factor which promotes the development of radiant energy to the highest possible temperature, and at the same time the portion I 4 is also heated by heat liberated from the heated gases in passing over and in intimate contact with the work surfaces. By introducing the heated gases into the gap I8 at a high velocity from the opening I|,"therefore, the continuous rush of newly formed heated products of combustion contributes to a high rate of heat input to the work. f

The heating unit I0 is extremely flexible in oppendentlyof and outside the heating units, can

v be arranged to be moved continuously in a single or several rows toward the heating station in any suitable manner. By having the slots II openended the work pieces I5 can be progressively moved to the heating units, so that the work pieces may be heat treated automatically in rapid succession. A suitable quenching station may be located adjacent to the heating station-whereby the metallic bodies may be cooled from an elevated hardening temperature by a suitable cooling medium, such as water, for example, so as to harden the same.

The heating unit of the invention is especially useful for heat treating or hardening work pieces of irregular shapes in an open arrangement. In each instance the slot or work receiving space may be of such shape that the refractory lining there- Of will conform to the shape of the portion of the work piece to be heat treated. Thus, in Fig. 3, a modification is illustrated for heat treating the rounded edge portion 30 of a work piece 3i. In this instance the body 20 of refractory material is shaped to form a recess 32 conforming to the shape of the edge portion 30 so that, when the edge portion 30 is positioned in the recess a narrow gap 33 is formed into which the heated products of combustion pass through the opening Il from the combustion chamber I8.

It may be advantageous in certain instances to locate the opening Il with respect to a definite part of the work piece to be heat treated. Such a modification is shown in Fig. 4 in which the opening Il is directly opposite a recess 34 in a die block 35 adapted to be heat treated. The heated gases discharged from the combustion chamber I8 through the opening I1 are directed against the walls of the recess 34 before spreading and fanning out in the narrow gap 36 to heat the lining 31 to a highly radiant condition.

In Fig. 5 is iilustrated'another modification in which the slot or receiving space 38 is formed with diverging walls to receive the toothed edge 39 of a saw blade 40. When using a gas mixture of air and ordinary city gas, and with the teeth of the sawv vblade positioned about inch from the diverging walls forming the refractory lining. it has beenpossible to heat the toothed edge 39 to the critical hardening temperature of 1650 F. in less than a minute, without heating to the hardening temperature parts of the blade 1/8 inch from the base of the teeth.

The dlverging walls of the slot 38 forman ex panding outlet in which turbulent flow of the heated gases may take place. Such turbulent flow or agitation of the heated gases, due to eddy currents produced in the expanding outlet, may be extremely beneficial in certain instances in that faster heat transfer to the work may be effected.

In view of the foregoing, it will now be understood that an improvement has been provided forselectively heat treating and hardening metallic` bodies or work pieces in an open arrangement. vBy providing a refractory lined recess or work receiving space in which the Work piece to be heat treated may be positioned, a relatively large surface area of the work piece can be heated in a single heating operation with theuse of a considerably smaller high velocity stream of heated gases. Thus, the heat capable of being the work receiving space to a white incandescent heat, but the forming of a narrow gap between the work piece and the lining confines the heated gases to blanket the lining with such gases from which heat is also liberated directly to the work. Hence, selective heat treatment of work surfaces of relatively large area and of irregular shape can be eilected in a single application of heat and work in an open arrangement with theaidof a chamber having a refractory lining that is provided'on one side with an inlet opening and opposite said inlet opening having its walls shaped to receive the surface portions to be heat treated, the steps which include moving the surface portions close to the walls of the workreceivlng opening to form a narrow passage between the surface portion and the walls of said opening, forcing hot products of combustion at high velocity through said passage to heat the refractory lining of the chamber to incandescence, and

- imparting heat to said surface portions directly all surfaces to be heat treated are simultanen ously heated to an elevated temperature.

Since the work pieces are heated by radiant heat and also by heat liberated from heated gases whose chemical reaction of combustion is com-` pleted, the exact position that the work piece must assume in the work receiving space is not critical.- This is of practical importance when the heating unit i is incorporated in production line machinery for heat treating work pieces in rapid succession, and all lof the work pieces do not occupy precisely the same position in the work receiving space of the heating unit during the heat treatingoperation.

This application is a division of my copending application Serial No.459,680, filed September 25, 1942, entitled Method of and apparatus for heat treating metallic bodies, now abandoned.

While several embodiments of the invention have been shown and described, it will be apparent that modifications and changes may be made without departing from the spirit and scope of the invention, as pointed out in the following claims.

What is claimed is:

1. In the art of heat treating surface portions of workpieces in an open arrangement with the aid of an open sided chamber having refractory walls that are provided with an inlet opening and opposite the inlet opening are provided with an opening having contours which receive the surface portions to be heat treated which includes the steps of moving the said surface portions into proximity to the contours to form therewith a narrow gap or passage surrounding the surface portions, introducing hot products of combustion at high velocity through said inlet into the passage to heat the side walls of the chamber to incandescence, maintaining the flow of the hot products of combustion to maintain the incandescence, and heating the surface portions by radiation from the incandescent walls of the chamber and the hot products of combus-l tion.

2. In the art of heating surface portions of from the incandescent walls and by convection from the hot gasses of combustion.

3. Apparatus for heat treating work in an open arrangement comprising a refractory body formed with a combustion chamber therein, said combustion chamber, being formed on one side with a plurality of openings through which a combustible mixture is to be introduced for combustion in said chamber, said chamber being formed at a point opposite said openings with a restricted opening through which the hot products of combustion are exhausted at high velocity from said chamber, said refractory body also being formed with a second chamber having one side open and having its walls shaped to receive snugly the surfaces to be heat treated of a workpiece, said restricted opening leading from said rst chamber to said second chamber at a point opposite the open side thereof and being substantially coextensive in length with said second chamber.

4. Apparatus for heat treating work of claim 3 in which said second chamber is formed with open ends whereby work may be moved continuously through said second chamber.

FREDERIC 0. HESS.

REFERENCES CITED lThe following references are of record in the file of this patent:

UNITED STATES PATENTS Number Name Date 1,617,609 Smith Feb. 15, 1927 1,688,705 Gray Oct. 23, 1928 1,981,850 Fisher Nov. 2'7, 1934 2,157,948 Beeny May 9, 1939 2,215,079 Hess Sept. 17, 1940 2,224,006 Day Dec. 3, 1940 2,273,809 Kinzei Feb. 17, 1942 2,303,408 Soderholm Dec. l, 1942 2,367,119 Hess Jan. 9, 1945 2,375,119 LeTourneau May 1, 1945 FOREIGN PATENTS Number Country Date 275,348 Germany June 15, 1914 105,294 Australia Sept. 23, 1938 

